1. Field of the Invention
The present invention relates to a capacitor for a semiconductor device and a manufacturing method thereof, and more particularly, to a capacitor having a metal-insulator-metal structure (hereinafter, referred to as a MIM capacitor) and a manufacturing method thereof.
2. Description of the Related Art
As semiconductor technology evolves, the area occupied by each device on a chip gradually decreases due to an increase in integration density. Such devices include capacitors, which for example are responsible for storing information on a dynamic random access memory (DRAM). Capacitors are required to maintain large capacitance values, even though integration requires there area to continue to decrease.
A number of methods have been proposed for achieving integration of capacitors These include: broadening the surface area of an electrode by forming a capacitor electrode in a three-dimensional shape such as a cylindrical shape, a fine shape, or the like; forming hemispherical grains (HSG) on the electrode surface; reducing the thickness of the dielectric film, and employing a high dielectric material having a high dielectric constant or a ferroelectric material as the dielectric film in the capacitor.
In the case where a material having a high dielectric constant, for example, Ta2O5 or BST((Ba,Sr))TiO3), is used as the dielectric film, it is difficult to use polycrystalline silicon, which is used as an electrode material in the prior art, to form an electrode, since a reduction in the thickness of a dielectric film causes tunneling, thereby increasing leakage current in the device. The leakage current can be mitigated/prevented by sandwiching a film having a low dielectric constant, such as, SiON, between a polycrystalline silicon electrode and a dielectric film. However, this method results in degradation in the total capacitance.
Hence, a capacitor, which uses a metal having a high work function, such as, TiN or a platinum-family metal such as Pt, instead of polycrystalline silicon, as an electrode material, has been proposed. Korean Patent Laid-Open Publication Gazette No. 2000-3511 discloses an MIM capacitor in which a Ta2O5 dielectric film is sandwiched between upper and lower electrodes made of TiN or Pt.
However, in a TiN/Ta2O5/TiN capacitor, the material, TiN, of upper and lower electrodes reacts with the Ta2O5 layer of the dielectric film when they are deposited or when they undergo a subsequent thermal treatment, resulting in deterioration of capacitor characteristics. This reaction can be prevented by interposing a reaction-preventing film of a low dielectric material such as Si3N4 between the dielectric film and each of the upper and lower electrodes. However, this also leads to a degradation in the capacitance and results in a rather complicated manufacturing process.
In a Pt/Ta2O5/Pt capacitor, there are no reactions between the dielectric film and upper and lower electrodes, but the use of a Pt-family metal is relatively expensive. In particular, deposition techniques providing a good step coverage necessary for forming an electrode in a three-dimensional shape, and simple etching techniques to achieve patterning at a low cost are not put into practical use, so that they are inadequate for mass production.
When a particular material is used as upper and lower electrodes and as a dielectric film of a capacitor, the increase in the leakage current and the degradation in the capacitance must be prevented, and also the stability, uniformity and long reliability necessary for mass production must be guaranteed. Furthermore, the economic efficiency must be satisfied. Therefore, despite recent improvements such as the adoption of various materials, as described above, the capacitor must be continuously improved in terms of practical utilization.
To address the above limitations, it is an object of the present invention to provide a capacitor which satisfies all of the aforementioned characteristics.
Another object of the present invention is to provide a method of manufacturing a capacitor which satisfies all of the aforementioned characteristics.
To achieve the first object, the present invention provides a capacitor in which a dielectric film is formed of a high dielectric material, a lower electrode is formed of a refractory metal such as Ti, Ta and W, or a conductive compound including the refractory metal, such as TiN, TiSiN, TiAIN, TaN, TaSiN, TaAlN and WN, and an upper electrode is formed of a platinum-family metal such as Ru, Pt or Ir, or a platinum-family metal oxide such as RuO2, PtO or IrO2.
Preferably, the high-dielectric material is Ta2O5, Al2O3 or TaON.
A reaction prevention film can be further included between the lower electrode and the dielectric film, to prevent the reaction between the material of the lower electrode and that of the dielectric film. The reaction prevention film is preferably formed of Si3N4, Al2O3, TaON, HfO2 or ZrO2.
To achieve the second object, the present invention provides a method of manufacturing a capacitor, including: forming a lower electrode of the above-described refractory metal or the above-described conductive compound including the refractory metal on a substrate; forming a dielectric film of the above-described high dielectric material on the lower electrode; and forming an upper electrode of a platinum-family metal or a platinum-family metal oxide on the dielectric film.
Here, it is preferable that the upper or upper electrode is formed by chemical vapor deposition (CVD) or atomic layer deposition (ALD). In particular, these deposition techniques are preferable to form a three-dimensional electrode such as a cylindrical electrode.
The dielectric film can have improved electrical characteristics by undergoing a thermal treatment or plasma process immediately after the dielectric film is formed or after an upper electrode is formed.
Also, the dielectric film can be formed in multiple steps by repeating deposition and thermal treatment or plasma processing for improving the electrical characteristics.
After the step of forming a lower electrode, a reaction prevention film can be formed to prevent the reaction between the material of the lower electrode and that of the dielectric film. Preferably, the reaction prevention film is formed by depositing one among the above-mentioned materials to be in an amorphous state. It is also preferable that, when a reaction prevention film is formed, thermal treatment for crystalizing the dielectric film is further performed after an upper electrode is formed.
According to the present invention, as described above, a refractory metal, which is relatively easy to deposit and pattern, or a conductive compound including a refractory metal, is used to form a lower electrode, and a platinum-family metal or a platinum-family metal oxide, the electrical properties of which is suited for a high dielectric material, is used to form an upper electrode. Thus, a capacitor, which satisfies many characteristics such as a negligible leakage current, high capacitance and the suitability for mass production, can be obtained.